We have developed immunoliposome technology for targeted intracellular drug delivery. Immunoliposomes (ILs) were designed to provide maximal efficacy via a receptor-targeted and internalizing drug carrier that is stable, long circulating, non-immunogenic, and versatile. We have previously constructed anti-HER2 ILs, which showed efficient binding and internalization in HER2-overexpressing cells in vitro and in vivo; immunoliposomes loaded with doxorubicin (anti-HER2 ILs-dox) demonstrated marked antitumor efficacy in multiple HER2-overexpressing models. Anti-HER2 ILs-dox has been systematically optimized with respect to each component (MAb fragment, liposomal drug, conjugation method) and developed for clinical trials. The modular organization of immunoliposome constructs makes possible a combinatorial strategy for the generation of new therapeutics: monoclonal antibody (MAb) fragments, derived from available MAbs or newly selected from phage antibody libraries, can be coupled to an appropriate liposomal drug, chosen from a repertoire of liposomal drugs. We will therefore apply this platform technology to develop new agents, and will prioritize these for highest clinical potential and rapid development. Our specific aims are to (1) complete advanced preclinical studies and clinical translation of anti-HER2 ILs-dox. We will collaborate with NCI and a new pharmaceutical partner to complete GMP manufacturing, formal toxicology, and IND filing. In parallel, we will develop assays of binding, internalization, and drug delivery that can be applied to clinical studies for mechanistic evaluation, which will be performed in collaboration with the newly awarded Molecular Assessment Program at UCSF. (2) Develop anti-HER2 ILs for targeted delivery of additional anticancer drugs. Anti-HER2 immunoliposomes can be used to deliver potent small molecules in addition to doxorubicin, including other FDA-approved chemotherapeutic drugs as well as novel compounds that we have recently encapsulated in liposomes. (3) Develop immunoliposomes targeted to other breast cancer-associated antigens, anti-EGFR ILs. We have constructed anti-EGFR immunoliposomes, using available MAbs and newly selected scFvs, and will evaluate them for EGFR-targeted drng delivery. (4) Develop immunoliposomes targeted to tumor-associated endothelial antigens, anti-VEGFR2 ILs. We have constructed anti-VEGFR2 immunoliposomes and will evaluate them for VEGFR2-targeted drug delivery in endothelial cells. (5) Implement clinical translation of new construct(s). Immunoliposome agents that appear the most promising based on Aims 2-4 will be moved to a development track for clinical testing,using our established production protocols and model for collaborative drug development.